Thin-film microelectromechanical device fabrication process

ABSTRACT

Processing and systems to create, and resulting products related to, very small-dimension singular, or monolithically arrayed, semiconductor mechanical devices. Processing is laser performed on selected semiconductor material whose internal crystalline structure becomes appropriately changed to establish the desired mechanical properties for a created device.

RELATED APPLICATIONS

This application is a Divisional application of a patent applicationentitled, MICROELECTROMECHANICAL THIN-FILM DEVICE, invented by JohnHartzell, Ser. No. 11/058,501, filed Feb. 14, 2005 now U.S. Pat. No.7,230,306, which is a continuation of an issued patent applicationentitled, SEMICONDUCTOR CRYSTAL-STRUCTURE-PROCESSED MECHANICAL DEVICESAND METHODS AND SYSTEMS FOR MAKING, invented by John Hartzell, Ser. No.10/131,057, filed Apr. 23, 2002, now U.S. Pat. No. 6,860,939. Theseapplications are incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

The present invention arises from a new area of recognition anddevelopment focussed on the technology of low-temperature,crystalline-structure-processed devices, and in particular mechanical,mechanical and electrical, so-called MEMS (micro-electromechanical),layered and stacked devices, and devices organized into monolithicarrays in layers, that opens up a broad new field of potential devicesand applications not heretofore so inexpensively and conveniently madepractical and practicable. This new field of possible devices, fromwhich a number of inventions, one of which is specifically addressed inthis disclosure, springs effectively from the recognition that internalcrystalline-structure processing performed within the bodies of a widevariety of different materials, is capable of enabling fabrication ofsmall (perhaps even down to devices formed from small molecularclusters), versatile, widely controllable and producible, accurate,mechanical, electromechanical and MEMS devices that can be formed veryinexpensively, and, with respect to laser processing, in uncontrolledand room-temperature environments not requiring vacuum chambers, etc.

Especially, the invention offers significant opportunities for thebuilding, relatively cheaply and very reliable, of very tinysemiconductor mechanical devices that can be deployed in densetwo-dimensional and three-dimensional complex arrays and stackedarrangements. These devices can take on a large range of differentconfigurations, such as individuated, single-device configurations,monolithic single-layer array arrangements of like devices, similarmonolithic arrays of combined electrical and mechanical devices, and invertically integrated and assembled stacks and layers of complexdevices, simply not achievable through conventional prior art processesand techniques. By enabling room-temperature fabrication, otherwiseeasily damaged and destroyed layer-supporting substrates, includingfabricated-device under-layers, can readily be employed.

The field of discovery and recognition which underpins the inventiondisclosed herein, can be practiced with a very wide range ofsemiconductor materials in arrays that can be deployed on rigidsubstrates of various characters, and on a wide range of flexiblematerials, such as traditional flex-circuit materials (polymers andplastics), metallic foil materials, and even fabric materials.Additionally, the field of development from which the present inventionemerges can be employed with large-dimension bulk materials, as well aswith various thin-film materials. The present invention is described inthis broader-ranging setting. With regard to the latter category ofmaterials, the process of this invention can take advantage oftraditional thin-film semiconductor processing techniques to shape andorganize unique devices, which are otherwise prepared in accordance withthe internal crystalline-structure-processing proposed by the presentinvention, thus to achieve and offer mechanical properties in a broadarena of new opportunities.

In this setting, the invention disclosed in this document isspecifically related to crystal-structure-processed semiconductormechanical devices, either as individuated, single devices, or in arraysof devices organized into monolithic, layer-type arrangements, as wellas to methodology and system organizations especially suited to thepreparation and fabrication of such devices. The invention proposed aunique way, employing, for example, different types of lasers and otherillumination sources. effectively to “reach into” the internalcrystalline structures different semiconductor materials for the purposeof controllably modifying those structure to produce advantageousmechanical properties in devices, and at sizes very difficult andsometimes not even possible to create via prior art techniques.

From the drawings and the descriptions which now follow, it will becomereadily apparent how the present invention lends itself to the economic,versatile, multi-material fabrication and use of a large variety ofdevices, ranging from relatively large devices to extremely small device9as mentioned earlier), and including various forms of MEMS devices,without the fabrication of these devices, insofar as laser processinginvolved, necessitating the use of special controlled processingenvironments, or surrounding processing temperatures above typical roomtemperature.

With this in mind, the significant improvements and specialcontributions made to the art of device-fabrication according to theinvention will become more fully apparent as the invention descriptionwhich now follows is read in conjunction with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block/schematic view illustrating a system which implementsthe methodology of this invention for the creation of single or arrayedsemiconductor mechanical devices in accordance with the presentinvention.

FIG. 2 is a schematic diagram illustrating single-side, full-depthinternal-crystalline-structure laser processing to create asemiconductor mechanical device in accordance with the invention.

FIG. 3 is very similar to FIG. 2, except that here what is shown istwo-sided processing according to the invention.

FIG. 4 is a view similar to FIG. 2, but here showing processingoccurring from an opposite side of material in accordance with theinvention.

FIG. 5 is a view illustrating single-side, partial-depthinternal-crystalline-structure processing according to the invention.

FIG. 6 is similar to FIG. 2, except that here single-side processingincludes a flood, or wash, of general heating illumination according toone form of practicing the invention, with this illumination strikingmaterial on what is shown as the upper side in FIG. 6.

FIG. 7 is similar to FIG. 6, except that it illustrates two-sidedprocessing wherein a relatively translated laser beam processes theupper side of material as pictured in FIG. 7, and a wash, or flood, ofother illumination (from a laser or another light soruce) aids from thebottom side of material as pictured in FIG. 7. FIG. 7, in particular,illustrates a condition where material that is being processed inaccordance with the invention is resting on a substrate which is nottransparent to the wash of illumination coming from the bottom side ofFIG. 7.

FIG. 8 is similar to FIG. 7, except that here the material beingprocessed is resting on a substrate, such as glass, which is essentiallytransparent to a wash of illumination striking from the bottom side ofFIG. 8.

FIGS. 9 and 10 illustrate two different views of a stylizedmicro-cantilever beam structure (mechanical device) constructed inaccordance with the invention.

FIG. 11 shows an isolated view of a single micro-cantilever mechanicalbeam structure with a darkened region presented in this figure toillustrate, variously, sensitizing of a surface of the beam for thedetection of a mechanical event, a chemical event, a biological event,etc. and also generally suggesting how, nested within the mechanicalmaterial making up the cantilever beam of FIG. 11 an electronicstructure, such as a transistor, could be formed in a portion of thecantilever beam.

FIG. 12 is a view illustrating single-side, full-depth internalcrystalline-structure processing of bulk material in accordance with thepresent invention.

FIG. 13 is similar to FIG. 12, except that here what is shown issingle-side, partial depth, bulk-material processing. FIGS. 12 and 13are included to give a broad understanding of the underlying overallfield in which the present invention finds its place.

FIG. 14 is a view illustrating internal-crystalline-structure processingemploying a single-crystal seed which is employed to characterize theend-result internal crystalline structure that can be achieved in thematerial pictured in FIG. 14.

FIG. 15 is a stylized, schematic, isometric view illustratingfragmentarily a single planer array of plural mechanical devicesprepared in a single monolithic, generally planar structure inaccordance with the present invention.

In FIGS. 2, 3, 4, 5, 6, 7, 8, 12 and 13, the darkened regions in thematerial being processed represents the processed regions in thesematerials.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, and referring first of all to FIG. 1,illustrated generally at 20 is a system which is employed according tothe present invention to implement a methodology for processing theinternal crystalline structure of various different semiconductormaterials in accordance with the invention, and all for the purpose ofcreating one or more mechanical devices that are intended to performrespective, predetermined, pre-chosen tasks. Included in system 20 are ablock 22 which represents a suitably programmed digital computer, ablock 24 which is operatively connected to block 22, and whichrepresents the presence of appropriate laser structure and controls,such as beam-shaping and optics controls using optical or maskingmethods, fluency controls, angularity controls, and other, for definingthe functional characteristics of a appropriate laser beam shown at 26which is to be employed in accordance with the invention to produceinternal crystalline-structure processing of any one of a number ofdifferent semiconductor materials, as will be more fully mentionedbelow. In FIG. 1, a material for processing is shown generally at 28,with this material having a layer form, and being suitably supported onan appropriate supporting substrate 30 which rests upon, and is anchoredto, a three-axis translation table (a driven table) 32.

Table 32 is drivingly connected to a motion drive system, represented byblock 34 in FIG. 1, which drive system is under the control of computer22. This motion drive system, under the control and influence ofcomputer 22, is capable of translating table 32, and thus materialsupported on this table, in each of the three usual orthogonal axesknown as the X, Y, and Z axes, such axes being pictured at the rightside of FIG. 1. Very specifically, control over motion of table 32 isdirected by an appropriate algorithm 36 which is resident withincomputer 22, and which, fundamentally, is equipped to direct a laserbeam for processing in accordance with device configuration and deviceinternal mechanical properties that have been chosen and selected, andfor which algorithm 36 is especially designed.

The exact nature of the construction of computer 22, of controls 24, ofalgorithm 36, and of the driven table and the motion drive therefor,form no part of the present invention, and accordingly are not furtherdetailed herein.

Fundamentally, what takes place in the operation of system 20 to producea given type of mechanical device is that a user selects a particularkind of device to build, selects an appropriate size and configurationfor that device, and then determines what are the best and mostappropriate internal mechanical properties that should be created inthat device in order to enable it to function properly with respect toimplementing a selected task. In general terms, the semiconductormaterials out of which a particular material can be selected to producesuch a device are those whose internal crystalline structures areclosely linked to the material's mechanical properties. Specifically,the various useable semiconductor materials are those whose internalcrystalline structures can be modified by laser processing to producedesired mechanical properties for a device. Various materials withrespect to which the present invention can conveniently and verysuccessfully work will be discussed very shortly, but it might be notedat this point that these materials, with respect to their precursorstates, i.e. their states before processing, range from fully amorphousmaterials through and into a range of various categories ofpolycrystalline materials.

For example, practice of the invention can begin with precursor materialwhich can fit into any one of the following categories: amorphous,nanocrystalline, microcrystalline, and polycrystalline. All suchmaterials can be generally described as having an internal crystallinestructure which, initially in a precursor state, is less than singlecrystalline in nature.

Semiconductor materials which can very successfully be processed inaccordance with this invention include silicon, germanium andsilicon-germanium. For the purpose of further illustration in thisdescription, a manner of practicing the invention, and a device emergingfrom that practice, will be described in conjunction withfull-layer-depth processing of a precursor amorphous silicon material,which will thus be treated as the specific kind of material which ispictured at 28 in FIG. 1. Also for the purpose of focused illustrationherein, this precursor illustrative amorphous silicon material isdeployed as an appropriate thin layer on a glass substrate, which isdesignated by reference numbered 30 in FIG. 1. Other substratematerials, as will become apparent, may include quartz, various metals,plastics, flex materials, fabrics and others. All of these materialshave what are referred herein as relatively low melting (or destruction)temperatures which are well below the melting temperature of the siliconprecursor material.

As has already been suggested above, practice of the present inventioncan produce a wide variety of uniquely configured and constructedsemiconductor mechanical devices which can be extremely small in size,ranging down even to a small molecular cluster size. Devices which canbe produced include various MEMS devices, micro-mechanical devices thatare sensitized to act as sensors for various environmental events, suchas chemical and biological events, various motion elements generally,oscillating elements, cantilever beams, actuators, relay switches, andother devices.

With respect to formation of a particular device's three-dimensionalconfiguration, this can be done in any one of a number of conventionallyknown ways. The exact processes employed to give three-dimensionaldefinition to a finally produced device, as for example to singulate anelement from a mass of material in which it has been formed, and/or toindividuate (for performance purposes) plural devices in a monolithicarray of devices, can take the form of various conventional processeswhich form no particular parts of the present invention. Thus they arenot discussed herein in detail.

For the purpose of illustration herein, processing will be described inthe setting, initially, of creating a single micro-mechanical cantilevermechanical device, using single-side, translated laser-beam processing.While various specific types of lasers can be employed such as a excimerlaser, a solid-state laser, a continuous-wave laser, and a femto laser,to name several, description will proceed in the context of using anexcimer laser.

Describing now a typical practice implemented by the present invention,an amorphous silicon layer having an appropriate precursor thickness issuitably formed on the surface in a glass substrate, such as substrate30. This assembly is placed on table 32 with appropriate initialalignment, and is then translated relatively with respect to a laserbeam, such as excimer laser beam 26, which beam is pulsed duringtranslation of the material relative to the source of the laser beam, toproduce full-depth, small-area quick melting and re-crystallizing of thesilicon material. An appropriate excimer laser, driven and pulsed at anappropriate pulse rate, and with an appropriate fluency and footprint inthe sense of how and with what outlines it strikes the surface of theamorphous silicon material, is directed toward this surface under thecontrol of computer 22, algorithm 36, and controls 24.

In accordance with the desired end-result internal crystallinestructure, and in a relative motion sense, the impingement point of thisbeam from a laser is moved in a defined way over the surface of theamorphous silicon material to produce rapid, full-depth melting andre-crystallizing in a manner designed to achieve the pre-determineddesired internal crystalline structure. Employing an excimer laser inthis fashion allows one to process material in such a fashion that thehigh-temperature events are essentially confined very locally to theregions specifically where material melt is occurring. Very little, andno dangerous, temperature rise occurs in the surrounding area, such aswithin substrate 30, and the whole process can take place in a normalatmospheric environment and completely at room temperature.

FIGS. 2, 3 and 4 show several different approaches to implement suchlaser processing. In FIG. 2 the laser beam strikes the surface of theamorphous silicon material on the upper side which is spaced away fromsupporting substrate 30. Processed material is indicated (darkened) at27. In FIG. 3 dual-sided processing takes place with two laser beamscooperating on opposite sides of the material, with the lower beameffectively processing the underside of the silicon material through thetransparency afforded by glass substrate 30. Such dual-sided laserprocessing effectively allows melting and re-crystallizing to take placesimultaneously on opposite sides of the supported silicon material, andwith each laser, therefore, requiring only a portion of the powerrequired for similar processing to take place under the influence of asingle laser beam. Where a mask is employed for beam shaping, thisdual-laser approach promotes longer-term durability of such a mask—atypically expensive device, and which is subject to significantdegradation at high laser power levels Two-sided dual-beam processingcan also be effective to allow processing to be performed in otherwisedifficult to reach areas with just a single processing beam.

In FIG. 4 single-side processing is demonstrated where, in this case,the processing laser beam is directed toward the silicon material fromthe bottom side (i.e. the substrate supported side) of this material.

FIG. 5 illustrates single-side, less than full-depth processing of thesilicon material, here employed to create ultimately a mechanical devicewhich effectively becomes a device that is composited with unprocessedmaterial lying beneath it, as illustrated in FIG. 5.

FIGS. 6, 7 and 8 show different manners of modifying the kinds of laserprocessing illustrated in FIGS. 2-4 inclusive, and specifically amodified processing approach which employs an additional broad area washof illumination 38 from another illumination source which could be, butis not necessarily, a laser source. In FIG. 6 this wash of illuminationstrikes the upper side of the silicon material in companionship withlaser beam 26, and is effective essentially to create an overalltemperature rise in the silicon material which permits a lower energylaser beam to perform appropriate full-depth processing. In FIGS. 7 and8 this wash 38 of illumination is directed toward the underside of thesilicon material and the supporting substrate, with FIG. 7 illustratinga condition where the substrate support material shown at 40 is nottransparent to illumination. In this implementation of the invention,the silicon material which is being processed is heated in a conductionmanner through heating of substrate 40. In FIG. 8, glass substrate 30 isagain pictured, and here, the wash 38 of illumination passes throughthis substrate to heat the silicon material above the substratedirectly.

According to practice of the invention, once a particular semiconductormechanical device to build has been decided upon, the desired threedimensional configuration of this device is chosen, and algorithm 36 isdesigned to direct laser processing in such a fashion as to create aregional volume of material within the processed material on thesubstrate adequate for the ultimate individuation and singulation, ifthat is what is desired, of an end-result mechanical device. With such achosen device configuration in mind, the most desired internalmechanical properties are predetermined, and algorithm 36 is alsoconstructed so that it will control the operation of a laser beam, suchas beam 26, to produce internal melting and re-crystallization in orderto achieve an internal crystalline structure that will yield the desiredmechanical properties. In some instances, it may be more appropriate tocreate differentiated regions of crystalline structure within a devicebeing built in order to produce different specific mechanical propertiesin different within that material. Such is entirely possible utilizingthe processing approach which has just been outlined above.

FIGS. 9 and 10 show a side cross section and an idealized top plan viewof a stylized cantilever-beam mechanical device 42 which has been sodefined by processing within the body of silicon material 28.

FIG. 11, in an idealized fashion, isolates an illustration of cantileverbeam 42, and shows by way of suggestion, produced by the darkened patchwhich appears in FIG. 11, how an appropriate event sensor, such as achemical sensor, a biological sensor, and other kinds of sensors couldbe applied, in any suitable manner, to the beam so as to respond toselected environmental events in a manner which causes deflection in thebeam. The present invention is not concerned with the specific kinds ofsensitivity for which a device, such as beam 42, is to be prepared, andthus details of how sensitizing can take place are not presented herein.

FIG. 11 can also be read to illustrate yet another interesting componentoffering of the present invention which is that it is possible to createwithin the mechanical body of the device, such as cantilever beam 42, anelectronic device, such as a semiconductor transistor which can bethought of as being represented by the darkened patch appearing in FIG.11.

FIGS. 12 and 13 illustrate use of the invention to modify internalcrystalline structure inside a bulk material 43, either with afull-depth approach (FIG. 12) or with a partial-depth approach (FIG. 13)in accordance with the invention. These two figures are included here tohelp establish a part of the underlying background of this invention.

FIG. 14 illustrates still another processing approach which utilizes asingle-crystalline material seed 44 which rests in a tiny indentationformed in an appropriate layer 45 of a supporting material, such assilicon dioxide. See 44 lies adjacent an amorphous layer 50 of silicon.Laser processing takes place with initial illumination of the seed,followed by the laser-beam progression from the seed in a definedpattern over the amorphous silicon material. This action causes thesingle crystalline character of the seed 44 to become telegraphed intothe internal structure of silicon layer 50, thus to characterize theinternal crystalline structure in this layer to make it more nearlysingle crystalline in structure at the conclusion of processing.

FIG. 15 illustrates, in simplified fragmentary form, a monolithic layerstructure 52 of processed, initially amorphous material which as beenprocessed in an array fashion, and at discrete locations, to create amonolithic array of mechanical devices such as the devices shown at 54.While it is certainly possible that each and every one of devices 54 isessentially the same in construction, and intended to perform the samekind of function, it is entirely possible, according to practice of theinvention, to differentiate the functionalities and thus the structuresof these arrayed elements.

It should thus be apparent that a unique process capable of creating awide range of unique mechanical devices, down to small molecular clusterdevices, with a high degree of precise control over internal mechanicalproperties, is made possible by the present invention. Also madepossible is the opportunity to do this insofar as laser processing isinvolved, in a completely atmospheric environment and at roomtemperature, and also in a manner which is one that does not attack anddestroy supporting structure, such as substrate structure.

Accordingly, while several embodiments and manners of practicing theinvention, and a system for doing all of this, have been illustrated anddescribed herein, it is appreciated that variations and modificationsmay be made without departing from the spirit of the invention.

1. A method for forming a microelectromechanical system (MEMS) thin-filmdevice, the method comprising: providing a substrate; forming aprecursor material overlying the substrate; laser annealing theprecursor material; selectively crystallizing regions of the precursormaterial; in response to selectively crystallizing, modifying themechanical properties of the regions; and forming a mechanical devicewith a mechanical body in the modified regions; wherein selectivelycrystallizing regions of the precursor material includes: directing anexcimer laser beam at a surface of the precursor material; shaping thebeam using a mask; and crystallizing a region of the precursor materialusing the shaped beam.
 2. The method of claim 1 further comprising:forming an electronic device within the mechanical body.
 3. The methodof claim 2 wherein forming the electronic device within the mechanicalbody includes forming a transistor.
 4. The method of claim 2 whereinforming the mechanical device with the mechanical body includes forminga mechanical body with a material having a first crystalline structure;and wherein forming the electronic device includes forming theelectronic device from a material having a second crystalline structure.5. The method of claim 4 wherein the first crystalline structure isdifferent from the second crystalline structure.
 6. The method of claim4 wherein forming the mechanical body and the electronic device includesforming the mechanical body and electronic device from the samematerial, with the first crystalline structure being different than thesecond crystalline structure.
 7. The method of claim 2 wherein formingthe mechanical device with the mechanical body in the modified regionsincludes forming a cantilever beam; the method further comprising:sensitizing the cantilever beam to an environmental stimulus.
 8. Themethod of claim 7 further comprising: the cantilever beam reacting to anenvironmental stimulus; the electronic device responding to reactions inthe cantilever beam.
 9. The method of claim 7 wherein the cantileverbeam is sensitized to react to a stimulus selected from the groupincluding motion, chemical, and biological.
 10. The method of claim 1wherein modifying the mechanical properties of the regions includesmodifying mechanical properties in response to changing the regions froma first crystalline structure to a second crystalline structure.
 11. Themethod of claim 1 wherein forming the precursor material overlying thesubstrate includes forming a material selected from the group includingsilicon, germanium, silicon-germanium, dielectrics, copper, silicondioxide, aluminum, tantalum, titanium, and piezoelectric materials. 12.The method of claim 1 wherein providing the substrate includes providinga substrate material selected from the group including glass, quartz,plastic, metal, flex materials, fabrics, copper foil, metal foil, andlow-melting temperature materials.
 13. The method of claim 1 whereinselectively crystallizing regions of the precursor material includes:crystallizing a surface region of the precursor material; and leavingmaterial underlying the surface region unprocessed.
 14. The method ofclaim 1 wherein selectively crystallizing regions of the precursormaterial includes crystallizing internal regions of the precursormaterial.
 15. The method of claim 1 wherein forming the precursormaterial overlying the substrate includes depositing a thin-film. 16.The method of claim 1 wherein forming the mechanical device with themechanical body in the modified regions includes forming a mechanicaldevice selected from the group including a cantilever beam, anoscillating element, an actuator, and a relay switch.
 17. A method forforming a microelectromechanical system (MEMS) thin-film device, themethod comprising: providing a substrate; forming a precursor materialoverlying the substrate; laser annealing the precursor material;selectively crystallizing regions of the precursor material; in responseto selectively crystallizing, modifying the mechanical properties of theregions; forming a mechanical device with a mechanical body in themodified regions; forming an electronic device within the mechanicalbody; wherein forming the mechanical device with the mechanical body inthe modified regions includes forming a cantilever beam; and, the methodfurther comprising: sensitizing the cantilever beam to an environmentalstimulus.
 18. The method of claim 17 wherein forming the electronicdevice within the mechanical body includes forming a transistor.
 19. Themethod of claim 17 wherein modifying the mechanical properties of theregions includes modifying mechanical properties in response to changingthe regions from a first crystalline structure to a second crystallinestructure.
 20. The method of claim 17 wherein selectively crystallizingregions of the precursor material includes: directing an excimer laserbeam at a surface of the precursor material; shaping the beam using amask; and crystallizing a region of the precursor material using theshaped beam.